[ntp:questions] Re: Questions about using GPS receiver to synchronize PowerBook G4

Bjorn Gabrielsson bg at lysator.liu.se
Sun Mar 27 19:30:57 UTC 2005


Ningyu Liu <nul105 at psu.edu> writes:

> Hello,
> 
> I need accurate timing (~1 ms) for an outdoor experiment. I have an
> Apple PowerBook G4 and plan to use a GPS receiver to synchronize its
> time. I have several questions about this issue.
> 1) Is the PPS signal necessary for the time synchronization? Can I get
> 1 ms accuracy from the NMEA message alone?

You will most likely need the PPS. NMEA messages will often "jump
around" depending on processor load in the receiver, no of satellites
tracked etc.

> 2) Since the PowerBook G4 doesn't have a RS-232 port, can I use a USB
> GPS receiver or a RS-232 GPS receiver with a USB adaptor?, or maybe a
> bluetooth GPS receiver?

To get the NMEA, yes I think that would work. The problem is getting
the PPS pulse onto a pin that can trigger an interrupt -- status pin
on serial port or the ACK pin on an parport.

> 3) Is there any other way to synchronize this laptop?

Does your laptop have an PCMCIA/PCCARD bay?  Try getting a serialport
PCCARD. I have used one from Socket, but not for timing
applications. YMMV...

Good luck!

-- Björn



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